Generally a website (ex: facebook, myspace) where people can add "friends", (generally people they may see once a day and never communicate with in person, or close friends they actually do associate with) and communicate with them through multiple ways such as leaving comments on posted pictures or blogs, or perhaps sending them a message they can read when they sign into the site at a later time.

Guy 1: I just joined a social networking site! It pwns!

Guy 2: Yeah right, social networking is the gayest thing to happen to Earth since reality tv.

(n.) A website that generally stopped the use of email. These websites rarely load, due to a constant server overload. They also ruined literacy of children by introducing the acronym.

(v.) When a person prefers to talk to their "friends" online instead of in person. Generally used by nerds who enjoy insulting others and not having the balls to insult them to their face. When this is used, that person is generally anonymous, due to the risk of being seen in public (which they really don't have to worry about, because they're always sitting in front of a computer). Social networking is also used by stalkers, due to the ability to appear as someone you are not. This tactic is also used by people who love hearing "omg ur soo hot lolol" and use a google picture, saying it is them.